As the popularity of multimedia has increased, the desire to distribute multimedia content, such as digital video, throughout a home or business using existing coaxial cable has also increased. One means for doing so is enabled by the use of devices developed, for example, according to the Multimedia over Coax Alliance (MoCA). Signals carrying multimedia content may enter a home or building at a point-of-entry (POE). From the POE, and within a home or building, such signals may be distributed to various terminals, or nodes that may be a part of a communication network, such as a broadband cable network (BCN), for example. Such terminals, clients, CPE'S, and/or clients, hereinafter referred to as clients, may be connected to, or included within, various entities, such as cable converter boxes, televisions, video monitors, cable modems, cable phones, and video game consoles, just to name a few examples.
As defined herein, the term “client” may be used interchangeably with the term “node”, and the term “channel” may be used interchangeably with the term “link”. Links, or channels, to clients may utilize signaling techniques such as a bitloaded modulation scheme. As defined herein, bitloading refers to a process of optimizing the modulation techniques used to carry data over a set a carriers on a link to a node to increase throughput. For example, some BCNs use bitloaded orthogonal frequency division multiplexing (OFDM). According to OFDM, the information is modulated on multiple carrier signals (typically 244 carriers, of which some or all may be modulated with information) with a variety of different modulation schemes on each individual carrier. For example, some of the carriers may be modulated with QAM 32, some with QAM 16, some with QAM 8, and some with BPSK (Binary Phase Shift Keying). Such a technique considers channel characteristics such as, for example, length, quality, channel connections, and/or any other features of a channel to a client that affects transmission of a message transmitting thereon. A modulation technique is chosen, for example, to provide an optimum rate of data transfer over a channel while maintaining an acceptable bit error rate. Symbols are transmitted downstream from over a channel via the 256 carriers (or some subset of them), each carrier transmitting bits according to a respective modulation, such as QAM 16, QAM 32, BPSK, and so on.
As noted above, different channels may utilize different bitloaded modulation schemes because the channels may have different physical and/or electrical properties. Physically, channels to different clients from a transmission source may vary in length and, electrically, such channels may vary because of the paths through and reflections from various elements, such as cables, switches, terminals, connections, and other electrical components in the network. Transmission characteristics of a channel may be described in terms of a signal-to-noise ratio (SNR), a bit-error rate (BER), and/or power level of a signal received at a client such as a remote device, for example.
In some BCNs, data may be transmitted on a network in the form of data packets, which includes a header, preamble, and a payload, for example. Such a header may include information regarding characteristics of the payload and the intended recipient. The information may include source and destination node identification, packet type and subtype, just to name a few examples. A preamble, may be used by the physical layer to detect and receive a packet.
Symbols represent one or more bits of data that make up a header, preamble, and/or payload in the packets to be transmitted. Both a header and a payload include information that is interpreted by an NC and/or a client. For a downstream packet, for example, a header includes information describing which client is an intended recipient of a corresponding payload. Such information may be read by a recipient client.
Additionally, an inter-frame gap (IFG) may exist between data packets. A header, preamble, and an IFG comprise an overhead portion of a data packet that may be combined with that of another data packet by aggregating data packets together. Data transmission efficiency, or throughput, may be improved by such aggregation since a relatively smaller portion of an aggregated data packet may be used for a preamble compared to that of a single data packet. Accordingly, the ratio of data (payload) to overhead may be increased.
A network coordinator, or network controller (NC), may be positioned either upstream or downstream of a POE. For example, in some BCNs an NC is included in “Headend” equipment that is considered to be upstream of a BCN. Such an NC coordinates upstream and downstream signals, such as data packets, from/to each channel of a BCN, for example. If downstream data packets, for instance, are intended for a single client, an NC aggregates such data packets to improve throughput. Downstream data packets, however, may not be aggregated if such downstream data packets are intended for multiple clients, since different clients will almost always have channels with different bitloading patterns.